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Sunday, December 23, 2012

On different forums, I often find people asking for help in
calculating the required turns for a ferrite transformer they are going to use
in high-frequency/SMPS inverters. In a high-frequency/SMPS inverter, the
ferrite transformer is used in the step-up/boost stage where the low voltage DC
from the battery is stepped up to high voltage DC. In this situation, there are
really only two choices when selecting topology – push-pull and full-bridge.
For transformer design, the difference between a push-pull and a full-bridge
transformer for same voltage and power will be that the push-pull transformer
will require a center tap, meaning it will require twice the number of primary
turns as the full-bridge transformer.

Calculation of required turns is actually quite simple and I’ll
explain this here.

For explanation, I’ll use an example and go through the
calculation process.

Let’s say the ferrite transformer will be used in a 250W
inverter. The selected topology is push-pull. The power source is a 12V
battery. Output voltage of the DC-DC converter stage will be 310V. Switching
frequency is 50kHz. The selected core is ETD39. Remember that the output of the transformer will be high frequency AC (50kHz square wave in this case). When I refer to an output of high voltage DC (eg 310VDC mentioned above), this is the DC output obtained after rectification (using ultrafast recovery diodes configured as bridge rectifier) and filtration (using LC filter).

During operation, the battery voltage does not stay fixed at
12V. With high loads, the voltage will be less than 12V. With low loads and
near-fully charged battery, the voltage may be higher than 13V. So, it must be
kept in mind that the input voltage is not constant, but is variable. In
inverters, the battery low-cut is usually set at 10.5V. So, we’ll take this as
our lowest possible input voltage.

Vinmin = 10.5V

The formula for calculating the number of required primary
turns is:

For our push-pull transformer, this will be one-half the
required number of turns.

Npri means number of primary turns; Nsec
means number of secondary turns; Naux means number of auxiliary
turns and so on. But just N (with no subscript) refers to turns ratio.

For calculating the required number of primary turns using
the formula, the parameters or variables that need to be considered are:

Bmax – Maximum flux density in Gauss.
If you’re used to using Tesla or milliTesla (T or mT) for flux density, just
remember that 1T = 104 Gauss. Bmax really depends on the
design and the transformer cores being used. In my designs, I usually take Bmax
to be in the range 1300G to 2000G. This will be acceptable for most transformer
cores. In this example, let’s start with 1500G. So Bmax = 1500.
Remember that too high a Bmax will cause the transformer to
saturate. Too low a Bmax will be under utilizing the core.

Ac – Effective Cross-Sectional Area
in cm2. You will get this information from the datasheets of the
ferrite cores. Ac is also sometimes referred to as Ae.
For ETD39, the effective cross-sectional area given in the
datasheet/specification sheet (I’m referring to TDK E141. You can download it
from here:www.tdk.co.jp/tefe02/e141.pdf), the effective
cross-sectional area (in the specification sheet, it’s referred to as Ae
but as I’ve said, it’s the same thing as Ac) is given as 125mm2.
That is equal to 1.25cm2. So, Ac = 1.25 for ETD39.

So now, we’ve obtained the values of all required parameters
for calculation Npri – the number of required primary turns.

Vin(nom) = 12f = 50000Bmax
= 1500Ac = 1.25

Plugging these values into the formula:

Npri
= 3.2

We won’t be using fractional windings, so we’ll round off Npri
to the nearest whole number, in this case, rounded down to 3 turns. Now, before
we finalize this and select Npri = 3, we better make sure that Bmax
is still within acceptable bounds. As we’ve decreased the number of turns from
the calculated figure (down to 3.0 from 3.2), Bmax will increase. We
now need to figure out just how much Bmax has increased and if that
is still an acceptable value.

Vin(nom) = 12 f
= 50000 Npri
= 3 Ac
= 1.25

Bmax
= 1600

The new value of Bmax is well within acceptable
bounds and so we can proceed with Npri = 3.

So, we now know that for the primary, our transformer will
require 3 turns + 3 turns.

In any design, if you need to adjust the values, you can
easily do so. But always remember to check that Bmax is acceptable.

For example, if for construction difficulties, winding
3 turns + 3 turns becomes difficult, you may use 2 turns + 2 turns or 4 turns +
4 turns. Increasing number of turns won’t hurt – you’ll just be under utilizing
the core. However, decreasing number of turns increases Bmax, so
just recheck to make sure Bmax is okay. The range I’ve stated for Bmax
(1300G to 2000G) is just an estimate. It will work for most cores. However,
with many cores, you can go higher to decrease the number of turns. Going lower
will just be under utilizing the core, but may sometimes be required if number
of turns is too low.

I’ve started off with a set Bmax and gone
on to calculate Npri from there. You can also assign a value of Npri
and then check if Bmax is okay. If not, you can then increase or
decrease Npri as required and then check if Bmax is okay,
and repeat this process until you get a satisfactory result. For example, you
may have set Npri = 2 and calculated Bmax and decided that this was too high.
So, you set Npri = 3 and calculated Bmax and decided it was okay. Or you may
have started with Npri = 4 and calculated Bmax and decided that it was too low.
So, you set Npri = 3 and calculated Bmax and decided it was okay.

Now it’s time to move on to the secondary. The output of our DC-DC
converter is 310V. So, the transformer output must be 310V at all input voltages,
from all the way up from 13.5V to all the way down to 10.5V. Naturally,
feedback will be implemented to keep the output voltage fixed even with line
and load variations – changes due to battery voltage change and also due to
load change. So, some headroom must be left for feedback to work. So, we’ll
design the transformer with secondary rated at 330V. Feedback will just adjust
the voltage required by changing the duty cycle of the PWM control signals.
Besides feedback, the headroom also compensates for some of the losses in the
converter and thus compensates for the voltage drops at different stages – for example,
in the MOSFETs, in the transformer itself, in the output rectifiers, output
inductor, etc.

This means that the output must be capable of supplying 330V
with input voltage equal to 10.5V and also input voltage equal to 13.5V. For
the PWM controller, we’ll take maximum duty cycle to be 98%. The gap allows for
dead-time.

Thus 96 turns are required for the secondary. With proper
implementation of feedback, a constant 310VDC output will be obtained
throughout the entire input voltage range of 10.5V to 13.5V.

Here, one thing to note is that even though I took 98% as the
maximum duty cycle, maximum duty cycle in practice will be smaller since our
transformer was calculated to provide 330V output. In the circuit, the output will
be 310V, so the duty cycle will be even lower. However, the advantage here is
that you can be certain that the output will not drop below 330V even with
heavy loads since a large enough headroom is provided for feedback to kick in and
maintain the output voltage even at high loads.

If any auxiliary windings are required, the required turns can
be easily calculated. Let me show with an example. Let’s say we need an
auxiliary winding to provide 19V. I know that the output 310V will be regulated,
whatever the input voltage may be, within the range initially specified (Vinmin
to Vinmax – 10.5V to 13.5V). So, the turns ratio for the auxiliary winding can
be calculated with respect to the secondary winding. Let’s call this turns
ratio (secondary : auxiliary) NA.

I would say that’s great for an auxiliary supply. If in your calculations you come to a voltage that is too far off the required target voltage and thus greater
accuracy is required, take Vaux as something higher
and use a voltage regulator.

For example, if in our previous example, instead of18.875V we had gotten 19.8V but needed more accuracy, we could've used 24V or thereabouts and used a voltage regulator to give 19V output.

So, there we have it. Our transformer has 3 turns + 3 turns
for primary, 96 turns for secondary and 6 turns for auxiliary.

Here’s our transformer:

Calculating required number of turns for a transformer is
actually a simple task and I hope that I could help you understand how to do
this. I hope this tutorial helps you in your ferrite transformer designs. Do
let me know your comments and feedback.

1) 50kHz is enough for use with ferrite transformer. Frequencies between 20kHz and 100kHz are usually used, with 30kHz, 50kHz, 75kHz and 100kHz being common frequencies.

2) I assumed 220V instead of 230V. I was thinking of sine wave inverter. So, to obtain a sine wave with RMS 220V, the peak must be 220V * sqrt(2) = 311V [sqrt(2) means square root 2, which is equal to 1.4142135....]. So, I took 310V since the DC bus voltage will be the peak voltage. When SPWM (sinusoidal pulse width modulation) is carried out, you will receive an output of 220V.

yes thamid i have a small request i am trying to develope a 150w inverter with smps transformer ,plz give your mail or send me a mail to this sandy.nani5@gmail.com .i will send my circuit diagram to your mail ,plz verify it for my satisfaction.

dear tahmid Its really helpful for me I was designing boost converter for my solar home ups. I need help from after reading the following link http://tahmidmc.blogspot.in/2012/09/some-of-my-smps-circuits.htmlI was in need of LCR Mere circuit can you post the firmware and circuit.

i have idea to build power inverter 6kw out put and input voltage is 48vdc the output voltage is 240vac, but in here i want to use SMPS transformer to built and the power mosfet ,can you help me to have any idea to guide me to help on it ,thanks so keep and touch

Hi,Use SG3525 to feed into high-low side drivers that drive MOSFETs in full-bridge configuration. These MOSFETs will drive a ferrite transformer. Rectify and filter the output. That's the DC-DC stage done. AC conversion stage will depend on a lot of things, most important being the desired otuput. My hunch is that it's sine wave. So use microcontroller and high-low side drivers to generate SPWM and drive MOSFETs in bridge configuration. Filter the output of the bridge and you have a sine wave output!

I am planning on building a msps for a car amp. The amp requires a single 50v rail and 300watts.I rather design the smps to be able to deliver this power continously rather than applying some music coeficient.So, : 300w , 12v to single 50v (regulated) . My big problem is choosing the transformer core. To be more precise how do i know how much power can a core handle? I know this varies with the frequency but have no idea how to determine it.For example in here:http://www.irf.com/technical-info/refdesigns/iraudps1.pdf they use a 29mm ring core for 500w(or even 1kw if i understood corectly). I have this core witf 3F3 material http://www.farnell.com/datasheets/1595842.pdfWill this core be able to handle the 300W continously? Also for this core , Bmax should be 100mT?Thank you !

hi i really love your tutorials but i would like to ask how i would go about when in comes to winding transformers for switch mode power suppliesdoes the same rule apply and i would also like you to email me a h-bridge inverter circuit i would love to construct one for my final year project my email address is djultra0008@gmail.com thanks

The tutorial presented here is for switch mode power supplies. I had the push-pull and full-bridge SMPS transformers in mind when designing it. Of course, I had in mind a low voltage to high voltage converter, although the same idea/principle can be applied for high voltage to low voltage converter.

As for the H-bridge circuit, I suggest you do some research and design the circuit. If you're stuck somewhere, then I can try to help.

dude..!!! how do we know that ..specific core has specific gauss?? am using E55 core ..can u tell me how much gauss it will be?? and for e65 core also..?? please tell me how much gauss it will be??reply me soon

A core doesn't have a specific flux density. You choose what flux density the core is to be "operated". This is done by selecting the number of turns with respect to the applied voltage. A core has a limit up to which the flux density can be. This is usually quite a bit larger than 3000G. So, by selecting an operating max flux density in the range 1300G to 2000G, we're "playing it safe".

hi tahmid i have some h-bridge circuits i would like to share with you how can i get it across to you one involves the popular tl494 and the other involves the use of the use of the 556 and cd4013 and another involve the ir2153 chip i would like you to have a look at them and i need a few explanation on some areas my email is djultra0008@gmail.com thnks.

If you go through this tutorial here, you'll see that I've mentioned that the same calculation can be used for push-pull and full-bridge. The only difference will be that, where in a push-pull transformer, the primary consists of Npri + Npri turns, the full-bridge transformer will only have Npri turns for the primary - no center tap.

Hi Thamid . Can u please describe How to select a core for a certain power. suppose i need 500w output power, and i also have Ac an Al values form core datasheet, now how to calculate delivered power? Actually it will be very helpful for ur reader if you refer using to relation between area product, winding area and core area, You know what i mean. And thanks for a good artical

It should - just take the appropriate values from the datasheet. Although, I haven't thought of it before. It's intersting and it's good that you brought it up. It should work. But just to be sure, I'll research into it and let you know. In the mean time, you could do some searching too! You might learn something interesting!

thanks tahmid. just another issue, its not easy getting these ferrite transformer here let alone getting the datasheet. i use to try salvaging the ones from computer psu please how can i identify the type of transformer they are e.g etd39 or etd49 and so on. do you have experience with this pleae help out thanks.

Look for the datasheet, eg for ETD39 or ETD49. The number (eg 49 or 39) is dependent on the dimensions of the core. The preceding letters (ETD) denote the "shape" and type of transformer. So, by matching the dimensions of your core against the datasheet figures you can identify which core.

Common cores used in computer power supplies are EI33 (most popular) and ERL35.

sir plz given me inverter circuit diagram on this transformer....plz sir tahmid needed me inverter circuit diagram of this ferrite core transformer...this transformer of any not found circuit diagram now me.....

You can design the circuit yourself using the SG3525 PWM controller. I've written an article / tutorial regarding using the SG3525: http://tahmidmc.blogspot.com/2013/01/using-sg3525-pwm-controller-explanation.html

hello Tahmid keep the good work going. I am running into a lot of problems that only u can help me. I recalculated my primary turns for 24v transformer in the formular u gave but when I check I am getting nearly two times the secondary voltage i worked it out for Is there anything else to be changed in the formular other than the input nominal voltage from 12 to 24 v when working out the turns for the transformer. Thank u

Recheck the calculations carefully to make sure you've done them correctly.

Make sure you have an LC filter and a minimum load at the output. Don't measure the output voltage without load, feedback or LC filter. With no load, the output capacitor will charge to the peak voltage. Without the load and LC filter, you won't obtain the "averaging" desired and output will be too high.

hi tahmid thanks for your formula on calculating the primary and secondary turns for ferrite etd 39 core i understand the nominal voltage in which is 12 the switching frequency 50khz which is 50000 the bmax or flux density you choose to be 1500 and the core area 1.25cm2 to give 330V but i dont know how you arrive at the 10 to the eighth power or the number 4 placed in the formula could you please give an explanation on it because i would truely appreciate it and secondly if i am going to calculate the number of primary and secondary turns for the transformer to work from 24VDC do i just have to put in 24 as the nominal voltage in or there is other things in the formula that will have to be adjusted or changed i truely have high regards for your work time and your answers to our questions thanks again please give an answer at anytime within your convenience thanks

The 10^8 term comes due to conversion of the different units to "standard units", ie from cm^2 to m^2 and Gauss to Tesla. You can eliminate the term 10^8 if you use m^2 instead of cm^2 and Tesla instead of Gauss.

thanks tahmid i fully understand everything worked on my project and everything is working well but one more thing the 98% duty cycle you choose to calculate the number of secondary turns is it that you must use 98% or you can choose a lower duty cycle and whether the duty cycle is high or low what effect would it have on running home appliances thanks again you are the BOSS

hi tahmid my project has been successful so far but i need to get something clear about "FEEDBACK" i plan to have 288VDC at the output of my dc-dc converter with lc filter, feedback and a minimum load, so from pin 16 to pin 2 of the "SG3525" i put a 5k6 resistor thus voltage at pin 2 is 3.2, from the output of the dc-dc converter i put a 450k resistor to pin 1 and 5k from pin 1 to ground so the voltage at pin 1 and 2 are equal, so 450:5 would give a 90:1 resistance ratio, so 90*3.2 would be 288, NOTE BRIEFLY i am operating from 24VDC i made my calculations for primary turns using the formula, checked b max and everything is in acceptable position i know i need some headroom for "FEEDBACK" to work so i took 98% duty cycle and calculate 0.98*22.5 minimum voltage which gives 22.05, so i calculate my secondary turns by taking 308V:22.05=13.96 so 13.96*7 which is my number of primary turns gives 97.77 rounded off to 98 to be my number of secondary turns do you think my calculations is right? i am looking forward for your reply thanks again in advance and remember you are the BOSS......

I'll definitely write an article for wire selection. For now, know that you need to choose the wire such that it can carry the entire current without heating significantly. However, don't use thick wires. They'll suffer due to skin effect. Use multiple thin wires.

98% is the maximum duty cycle that I have taken to be allowable. This has been done to prevent cross-conduction between switching devices, which would result in a short-circuit. There isn't much of an advantage to using a lower duty cycle. The actual duty cycle will be much lower than this in normal operation, due to the implementation of feedback.

Hi Tahmid I think this is the best pratical inverter building forum on the internet u are teaching the world. I have been trying to put together an inverter over a year now and it since I saw ur blog I am getting some good results.I have three questions1 with no AC load on my h bridge should i be getting my 5v drive voltage on the gates of the fets in the dc-dc converter I am using one of ur drive circuits ( My voltage only comes on when a load is connected and increase with added load. off when there is no load ) ????? 2 My AC voltage increases with the amount of load I apply eg from 125 to 140v AC which stage could be giving me this problem I am using 556 and 4013 configurationThank u for ur ususal support

Thank u for your reply Thamid but i am not sure I got A Clear answer. I said I want to know if i should have the drive volt on the gate of the fet any at all with no load connected to the h bridge or only when a load is applied this voltage should come up on the gate. I am using a drive circuit similar to you figure 5 design the only difference is there is no 10k from base to ground on my circuit. Could u answer the other part of the question about the increase in AC voltage with increase load which stage could be giving me that problem . Thank you for usual support

The drive voltage doesn't show properly on the high-side due to the "virtual ground". If you must test it, remove the MOSFETs, connect VS to ground and test the voltage and frequency at HO with respect to ground. If all's well, remove the short from VS to ground and then connect the MOSFETs.

Regarding voltage difference, it'll be difficult to try to figure out where the problem lies without taking a look at the circuit diagram. Make sure that the driver circuit is working properly. It sounds like a problem in the driver circuit, even though nothing can be said with certainty without taking a look at the circuit.

I suggest that you, instead of using 556 and 4013, use SG3525. That will be better. Then, just feed the otuput of the SG3525 to the MOSFET high-low side drivers.

I hope you have received the answer to your questions. Feel free to ask if you have any query or doubt.

Thank you Thamid for your reply I will check to see my drive circuit is working properly. One more question which design is better to handle heavier loads the paralell or series transformer configuration in the dc to dc converter. Thank you for your support

I recommend using one transformer instead of multiple in series/parallel. However, if you must use more than one transformer, you should use the converters in parallel and not the transformers themselves. For example, if you're using push-pull topology and have two transformers, use two push-pull stages to drive both transformers, both from the same input signal. You can connect the outputs in parallel, with current limiting.

hi tahmid.i am new to this smps stuff.. i have been following all your you-tube posts and blogs on eda board... i am building a 1kw smps inverter according to the circuit diagram you gave in ur link... the only problem is that i am unable to find ft37-77 core.. so could u please help me by suggesting an etd core as an alternative to toroid core and ways to wind it with copper wire...i will be really thankful..

Could you please mention which link (1kW SMPS inverter) you are talking about?

You can choose one of the higher power ETD cores for this purpose. Some cores you may be able to use are ETD49, ETD54, etc. Of course, you need to keep in mind other factors such as winding, frequency, etc.

thanks a lot for responding tahmid... i am building a 1kw inverter based on push pull topology for the dc boost stage which is 12v to 32o v dc using ka3525 pwm chip as in ur link.. at 50 khz. initially i thought of using ft37-77 core but later realized i cant find them in here..i know very little about winding an ETD core so i thought if u could help in selecting an ETD and procedure for winding it...thnks again..

hi again tahmid my project is more successful as i go along, according to your blog on ferrite transformer turns calculation i now have a clear understanding on how to work it out with respect to voltage, frequency, bmax and all that, but there is a few things i want to get more clearly, my questions to you now is, at a switching frequency of 50 khz if i use 22 awg wire to wind the transformer, if i change my switching frequency to 75 khz do i need a smaller wire like about 26 awg to wind the transformer......? next do i have to use a higher switching frequency for a higher wattage inverter or it does not matter as long as the calculations are right...... thanks again for your usual support......

Yes, as switching frequency increases, you should look to use thinner wire.

Refer to this chart:http://www.powerstream.com/Wire_Size.htm

You can use a not too high frequency and just make sure that the calculations are correct. Keep in mind that the higher the switching frequency, the lower the required inductance, capacitance and transformer turns, but the higher the switching losses.

thanks tahmid all this really helps so to be more clear on all this you are saying its best to use a lower switching frequency for higher wattage inverters and one more thing, i have seen inverters with the transformers in parallel connection and some with the transformers in series connection, which do you think works better.......thanks again for your support......

hi tamid i designed a 47kz push pull 12v to 310v converter but there is problem i seem to be getting close to 500vdc when rectified i am using an ei33 core ripped from a computer power supply though i have not yet implemented the feedback yet i did all the calculation for the transformer and got 3 + 3 turns for primary and 100 turns for secondary i am wondering if is bcos i winded the primary turns first b4 secondary i chose 1600g as flux pls any help would be appreciated.

You have to use feedback. Without feedback, you'll be running at near 100% duty cycle which will mean very high voltages. Remember that the calculations are done, assuming that proper feedback is in place. The feedback circuitry is to regulate the output voltage depending on input line voltage and output load. The nominal operating duty cycle with correct feedback implementation will be quite a bit lower than 100%.

Hello Tahmid I have attached the inverter circuit to an email and sent it to ur email address. This is the circuit I am having the gate voltage problem with.Please check to see if there is a circuit error. Thank you

my question is :1. i use TL394 for produce 38kHz for drive the push pull. what the problem if i applied this transformer use push pull with frequency 38 kHz ? 2. can i produce 1500 Watt spms use this transformer at 38 kHz push pull?3. what a good frequency for this application ?

hi tahmid your blog has helped me out the most sucessful way, i have now managed to build a inverter using four dc-dc converters in parallel supplying 310vdc, could u point me to a h bridge circiut that i could build with eight mosfets so i could get 230vac, i really need this and thanks much again

I am extremely glad that my blog has helped you. I hope to make my blog even better to reach out to help many more people like you.

For the PWM controller, you can use SG3525. Set the frequency to 50Hz/60Hz as required. I've written a tutorial covering the use of the popular PWM controller SG3525. Check it out here:http://tahmidmc.blogspot.com/2013/01/using-sg3525-pwm-controller-explanation.html

For the MOSFET driver, you can use IR2110. I've written a tutorial covering the use of IR2110 for MOSFET drive in high-low side configurations (bridge configurations included). Check it out here:http://tahmidmc.blogspot.com/2013/01/using-high-low-side-driver-ir2110-with.html

hi again sir, is there any difference with the h bridge in a 12 volt inverter than that of a 24 volt or its just a standard circuit or the h bridge circuit is built according to the wattage of the inverter thanks........

No matter what voltage you use, the principle is obviously the same. 24V is preferred over 12V for higher powers due to the lower current (for the same power output). This makes component selection and even wire selection easier and due to the lower current, places less "stress" on the components as they need to handle half the current.

hi tamid here is a funny senario i built a 12v-310v dc-dc converter using an e-i33 core the funny thing here is when i read the ac output section with my meter it shows250v but when i read the dc section its giving me 500vdc is that the recovery diodes are recovering too fast or what ithe diodes i am using is mur460 pls if you have any solution it would be helpful thnks

hi tamid i wound a transformer with with 1 primary turn and 3 sec turns for a push pull. my bm is 2230 for 20khz 6 volt input 3.35cm2 core area. but i dont get any output at transformer can u plz help me

hi tamid do pls know how to manually calculate the area of an etd core ,well since where i live it difficult to buy one so i usually come across so many core but with no labeling so i don't know the core type or its area if you any solutions it would be helpful thnks

You can measure the dimensions of the core and match the values against the values of a standard datasheet to identify which core you have. That way, you can identify the core without needing to have labelling provided to you by your ferrite core supplier.

The transformer has a total of 6 turns primary, with a center tap. You take a wire. Join one end to one of the bobbin pins - A. Then wind three turns and join the other end to another bobbin pin - B. Take another piece of wire and join one end to the end B. In the same direction (clockwise/anticlockwise) in which you wound the first three turns, wind three more turns. Then attach the other end of the wire to another bobbin pin - C. A is one end that goes to a MOSFET "leg". B is the center tap that goes to the positive supply (since this is for a push-pull converter). C is the other end that goes to another MOSFET "leg".

hi tahmid thumbs up again for your blog, i need some help on selecting some mosfets for my dc-dc converter for a 600 watts inverter ( push pull topology } i use two irfz46n to drive my ferrite transformer but they heat and blow out in a short while...... the irfz46n is rated 50 amps so do i have to add more in parallel to my converter or do i need to purchase mosfets rated at higher amps for example irf3205 which is rated 110 amps and how much should i use, PLEASE i need your help or do you have a way to calculate and parallel mosfets to add up to a certain AMP for 600 WATTS ? PLEASE give me your most clear answer on this and keep up the good work thanks again BOSS ......

hi again tahmid thanks for your continued help my question to you is, i have a ferrite torodial core the effective cross sectional area in cm2 is 0.946 could i use it in the formula for my transformer calculations....thanks again

hi tamid in your replies on me getting about 500v dc you said i should place a load on the output and then implement feedback the question is how do i place a load on a 310vdc output and what kind of load are you talking about coz i dont have a load that will take such voltage i am buliding a small inverter and hope to build the circuit in sections thnks

my question is :1. i use TL394 for produce 38kHz for drive the push pull. whether any problem if i applied this transformer use push pull with frequency 38 kHz ?2. can i produce 1500 Watt spms use this transformer at 38 kHz push pull?3. what a good frequency for this application ?

hi tamid in terms of feedback implementation how do i calculate my duty cycle for instance using the sg3535 setting pin 2 to 2.5v as reference how do i calculate the resistor values for pin 1 for a lets say 90% duty cycle since these pins are responsible for the duty cycle thnks

That could be due to a lot of things. Without more information, it would be too difficult to understand what's causing the error.

Which controller are you using?Which driver are you using?Which topology are you using?Describe the feedback circuitry you're using.What are the input and output specifications? What frequency did you use?What did you select as the maximum duty cycle?Which MOSFETs are you using?Describe the transformer output section.Which transformer core are you using?What is your load?

hi Tamid, I,m bret from nigeria.. i really found your blog very useful since i discovered it. keep the good work. Pls i want you to tell me how to do the transformer turn calculation for an smps charger using the half bridge topology. my chager is to handle about 30Amps and 13.8V output frm 220Vac input.

Hello Tahmid, Your Transformer calculation post has help me a lot in designing DC-DC converter but recently I moved to DC_AC inverter. I can use the method you post here for my high frequency low voltage DC to High voltage DC (20-400 VDC)tranformer design which works very well, also for the 400v DC side filter inductor design I used the methods in Abraham pressman book and my filter works well, BUT I am having problems with my SPWM wave input to Sine Wave output filter inductor. I am not sure if I should use the same method of low pass filter inductor core design method used in DC filtering or is there any special consideration you have to take into account in design of magnetic material for SPWM filter inductor (for pure sine wave output). Sorry for the long wind post. Your help will be greatly appreciated.FaruqNigeria

For LC filter, choose values such that the resonant frequency is close to your output frequency. If your frequency is 50Hz, an LC filter with resonant frequency between 400Hz to 1500Hz should work well. Then you need to size the inductor and capacitor. Don't use too high an inductance - otherwise the output impedance will be very high. Don't use too high a capacitance - this will create rush currents.

Hello Thamid, I have a question about the equation to calculate an output inductor for a forward converter with a transformer (full bridge). I actually have several formulas and all of them are no the same. Which way do you use to calculate it?

Hi, TahmidDo you still check your hotmail mailbox from time to time , i would like some advice on winding high voltage secondaries.From what i saw in microwave smps, they seem to wind sections side by side instead of 1 layer over the other.

Tahmid, need clarification on something. Firstly, there is no guide on the internet that shows how to wind a ferrite toroid, yes?

Reason is, I`m trying to wind one, and then to test it out. Say my calculations state 5 turns primary, so that means two wires on the primary side, with the center two, linking them, serving as CT, yes?

Lastly, the secondary and primary is wound the in the same direction? Or can one just wound this bifilar style for primary, over the many turns of secondary? In my circuit I need a step up.

There is a big credit of transformer for getting us current constantly. We cannot think about current without transformer. So it is better to know about transformer for every people. Thanks for sharing the information of transformer.

thank you this information was very helpful to me i'm designing smps to convert from 12vdc to 220vac 50hzI'm wondering about what are the stages I should follow with arrangement using also I don't know how to calculate the suitable frequency for the circuitwhat is the most important element of the power supply I should choose first

how to calculate the gauge of the wire for your above given example of 3+3 turns & 96 turns xmer 50khz.can we apply P=VI & V=I(R+jXl) to find max ampere and accordingly the gauge or due to skin effect @ 50khz its better to use litz wire and if yes than of how many core wd respect to max current.

I made my transformer with 8 primary and 100 secondary turn 33KHz ETD29 (76mm^2) with 11V input. I get 10-15times more voltage while testing signal generator. However when I use the voltage (11V) coming from FET (bf245) I see 200mV on the output.what is the reason for that ?any help is appreciated

Nice to see ur blog. I am an electronics engineer working in thyristor based high current rectifiers. I am planning for design a high frequency rectifier for high current ranges with bridge rectifier construction. can u please guide me and help to design the same.

My questions are1. for low voltage high current DC output bridge rectifier is suitable??2. Can i follow your calculation for this rectifier??3. what is the maximum current i can get from high frequency rectifier??4. Any book which guide me for designing this system??

I have calculated a transformer for a Push-Pull SMPS that works with 12Vdc and the output is 410V. It has 2+2 turns in the primary and 56+56 in the secondary, with a EE4215 core. In my country I can´t found a company that make that transformer,

Did you ever wound a transformer like this? Any suggestion?

Thanks you very much and congratulations for your blog that is very useful.

Hi tahmid! thanks a million for all your efforts. Just got a question to ask: does the same principle apply to toroidal transformer(in smps). If no, then how do we calculate the relationship between input and output voltage?...pls assist. thanks

Hi Thahmid,Hope you are fine.Your blog is really helpful for me. I learned more from you.Now I am planning to design a Transformer-less Inverter using SG3525 in DC-DC and a PIC – PWM module for Sine wave production. I will be following your example circuit you mentioned with SG3525 for DC-DC conversion, but let me know what should be the wire gauge for the DC-DC converter transformer windings to make an inverter of 800W capacity. Please help me on this.Also please suggest isolation for the feedback in the circuit. I am afraid of 320V DC come out the inverter thru battery terminals.

Hi Thahmid,i have a power supply (180W DC12V 15A LED Single Output Switching Power Supply), i took this supply from junk yard for some experiment, i wound transformer as it is i opened but when i ON this supply is going heat too much but output voltage is ok then i put some load on it on series circuit on main, series lamp is ON and output is block, all components is ok FET is 7N60. ***i want to wind this transformer can u help me***** supply picture is http://www.4shared.com/download/bKbmAVCUce/PH_316.jpg?lgfp=1000

Hi tahmid i was designing a ferrite core transformer using push pull topology, 60KHz,primary turns-3,sec-turns-120. I generated my signal from SG3525 and IR2110.I pulled down the gate of the mosfets(IRF3205) with 1k resistor but still i am constantly having the mosfets burnt 5minutes after i connected it to the transformer although i did not implement feedback for now. what exactly do think could cause the problem. please help me out this mess.

Tahmid Hi, firstly I congratulate you for doing such a nice sharing sg3525 What is the formula of compensation capacitors, for example, you're using 10nF, other examples 220pF, 47nF, 100nF .... these values ​​are chosen according to what? thanks yılmaz kemancıI love sharing,,, my site http://picsimulatorideexample.wordpress.com/

Hello Tahmid! good blog, sounds lots of work behind...I'm working on a small inverter 200w. push pull bridge can feed 10Amps. But with no load i can reach 300-400Vac @60Khz.But I can't keep this voltage when a load is plugged i just can reach 60vac @ 30W...... My core is 2+2 primary 60 secondary.Could you tell me what kind of things can be responsible of this loss of power? i feed 8A@12VDC primary and i can just get merely 30W.... primary winding is 3X0.5mm² in parallel. Best regards. B.H@FRA

hii Tahmid! im so proud of your info , your so good and helpfull thanks for all of your info 1- i need to know which AWG wire in prim and sec wendings i can use to have output power 1000 watts ,(same core u used)2- can i turn couple or triple wires together to have higher current in prim turns (3 wires together 3 turns then another 3 for the other 3 turns)3- what to do with the sec. turns should i triple the wires as in the prim. ? im still confused because i read all ur comments but didnt find what can help , so i'll be so happy to know what i can do to get 1000 watt from the same core u used

hi tahmid.. i want to create pontential transformer for voltage measurement, with turn ratio of voltage in transformer...i choose ferrit core because my objeck have frequency in 40 kHz, am i can be used this technique for solving my problems?

Dear Tahmid,I am new in SMPS design.I want make simple adjustable SMPS labrotory power supply 1-30 volt and max 3 ampere Ebay have very cheap LM2596 or LM2576 Modules.is it possiable a pre simple circuit for working 220 volt AC for this module.I mean it must cheap and small and suitable but it must without power transformer thanks for replyRegards

Assala-mu-alaikum vai, I've a question about this article. Here you showed 3+3 centre tap primary and 96 turns secondery. If I need 3+3 centre tap primary and secondery also with centre tap than which modification required? Actually this question comes to see this two articles :http://homemadecircuitsandschematics.blogspot.com/2012/09/making-200-watt-compact-pwm-inverter.htmlandhttp://easy-electronic-circuits.blogspot.com/2014/05/100-watt-compact-ferrite-inverter.html

Dear sir nice postI have a doubt about the winding primary formule that gives 3.2. turns. in case 3.5, 3.6, 3.9 what should I do?I need to know what to do with that number before calculate secundary winding.

It can work as long as it remains complete after the breakage. If you loose even a small portion of the ferrite core, your whole inductance values will change and most likely the over-all behavior of your coupled inductor as well.

Hi I am using a E25*20*7 Ferrite core. The primary is 12 turns of 22 SWG. The secondary is 320 turns of 36 SWG. I would like to get 300-320 volts. I am using UC3843 and 50 khz frequency. But the output voltage is only 180 voltsWhat needs to be done

Hi tahmid your work so great-full. I recently planned to develop ups for my home. i learned concept ups from your post(MOSFET, Switching) and i have doubt in transformer selection, but you cleared well. One more request is to know about which types of transformer in push-pull stage and output stage as well as its different types and configuration

Good work with you tutoring. Your explanations are very will done and easy to understand.

I am trying to drive a high power ceramic transducer element using one of the latest TI class D chips. It is the TPA3116D2. This chip allows you to set the PWM frequency between 400 kHz and 1.6 MHz. With that in mind, The core size should get quite a bit smaller. Using the equation in this blog, the cross section becomes very small i.e. .2 cm 2. Any larger a cross section I get 1 turn or less for the primary. The TI part will allow PBTL connection providing up to 100 watts output power. My problem is making sure the impedance never falls below 1.6 ohms. The baseband signal is 25kHz but the PWM frequency can be greater than 400 kHz. The reactance of the ceramic element is tuned out by using a parallel inductor.

My question is, do you have any suggestions for the core and the kind of material. I assume the material should be suitable for operation above 400 kHz. I am trying to make the driver amplifier as small as possible and thus I need the smallest core that can handle the power but also present the reflected impedance greater than perhaps 2 ohms.

This application is just a variation of a SMPS but at higher frequencies than the 50 kHz circuits posted here.

Hi Tahmid,Thank you for the detailed explanation of HF transformer calculations. But I would like to build LF (low frequency) inverter 1kW using full bridge & SPWM control signals with app. 24kHz to obtain 50Hz 220VAC output. The problem is how to calculate the 50Hz transformer (EI iron core). I am going to use 12V battery but the available information I can find concerns LF inverter transformers but with higher input voltages (24V.... 48V).

The recomendation is:- for 48V DC system to use transformer with primary 24-30V

Following that recommendation I can calculate the primary for 12VDC system transformer to be app. 6 to 7,5V?

Please if you can to advise me how to calculate the needed transformer (EI or toroidal). It should maintain 220V all the way from 10,5-14V DC (the inverter has feedback line which regulates the SPWM duty).

Shop 12v Converter Inverter at Dctodcpower.com. The 12v inverter basically produces the same type of power that is created by utility companies and generators. When we have the confidence on the high quality of our products, we could offer very competitive prices at the same time.

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About Me

I am Syed Tahmid Mahbub, from Dhaka, Bangladesh, born on August 1, 1994.
Electronics is my passion and from class V, I have been learning electronics. I learnt and worked mostly on SMPS, power electronics, microcontrollers and integration of microcontrollers with SMPS and power electronics. I've used PIC and AVR microcontrollers - PIC 10F, 12F, 16F, 18F, 24F, dsPIC 30F, 33F, PIC32, ATmega and ATtiny, integrating them with various SMPS and power electronics circuits.
I have completed my Bachelor's degree from Cornell University (Class of 2017) in Ithaca, New York, USA, majoring in Electrical and Computer Engineering (ECE).
I am a member of the forum www.edaboard.com, where I am an "Advanced Member Level 5" (the highest level attainable) and also the forum allaboutcircuits.com, where I am a "Senior Member". I post to help solve electronics-related problems of engineers and engineering students from all over the world.
I love watching and playing cricket and football (soccer), and listening to music.
I am now a hardware engineer at Apple in Silicon Valley, California, USA.